Abstract: This invention is a unique single-site method of determining the local total electron content (TEC) of the ionosphere and its space-time variation using a global positioning system (GPS) ionospheric receiver. The TEC of the ionosphere is specified in terms of a space-time map of the local TEC in the vicinity of the receiver. Differential group and phase path data between two L-band frequencies (L1 and L2) for a plurality of the GPS satellites in view of the receiver station are analyzed by a least squares technique to extract both the ten parameters of a full second order space-time polynomial expansion for the vertical TEC (VTEC) and the differential delay biases associated with the space vehicles (SVs). The method is applicable to day and nighttime data.